This invention relates to the storage of fluids, and more particularly to wheeled vehicles for transporting different liquids in a given container.
When a tank truck or a railroad tank car transporting a particular gas or liquid is to be used to transport a different non-compatible fluid, it is necessary to clean the container of the vehicle. This is usually expensive and inconvenient, and the required specialized cleaning facilities frequently are not available. To solve this problem, it has been proposed that vehicles for transporting fluids be provided with a pair of separate inlets and outlets and a flexible diaphragm that alternately lines opposed sides of the vehicle's container. Movement of the diaphragm to line one side of the container provides a chamber for one fluid, and movement of the diaphragm to the opposite side of the container provides a chamber for a different non-compatible fluid. Thus, the container does not have to be cleaned to enable the vehicle to transport either of such fluids. However, there has not been any significant use of such vehicles having a diaphragm that enables them to alternately carry non-compatible fluids without being cleaned in between. One reason such vehicles have not been used has been the extensive modification of standard vehicles believed necessary to prevent damage to the diaphragm or to the vehicle container or components. For example, it is necessary that liquid transport vehicles have a specified minimum empty space or outage in their upper end. A visible gauge that projects into the vehicle tank has been used to identify the uppermost permissible liquid level in the tank. Such a gauge could not be used in a diaphragm vehicle because it could damage, or be damaged by, the diaphragm.